Positron Emission Tomography (PET) is an important imaging modality useful in the early diagnosis and therapy planning of many diseases. It has been demonstrated to be useful and cost effective in the assessment and diagnosis of a variety of heart and brain diseases. Moreover, with the recent development of whole body scanners, the field of oncology is opening up to PET. The availability of PET on a clinical basis helps physicians make therapy choices earlier in the treatment of the patient, thereby improving chances of therapeutic success, as well as reducing the costly work up required to make a clear diagnosis. However, due to the cost of opening and operating a PET center the technique is not widely available. The widespread availability of clinical PET will be strongly influenced by the development of a more economical and compact accelerator for generating PET radionuclides. Typically, the accelerator for producing PET radionuclides is a cyclotron. Generally, the terminal particle energy can be used as a significant determining factor in accelerator cost. An accelerator which utilizes lower bombarding energies (less than 8 MeV protons) and higher beam currents (greater than 100 uA) than that which is presently available, is necessary to minimize accelerator manufacturing costs.
As bombarding energies decrease, so do the number of available target materials that will produce the desired radionuclides in useful quantities. The four conventional PET radionuclides are carbon-11 (.sup.11 C), nitrogen-13 (.sup.13 N), oxygen-15 (.sup.15 O), and fluorine-18 (.sup.18 F).
Most cyclotron targets now in operation take the form of a single phase continuous material, i.e., the material under bombardment is in a completely gaseous, liquid or solid form. Several single phase targets require further processing to release or to make the clinically useful radionuclides. Further, the target materials are limited in the variety of PET radionuclides which can ultimately be produced.
Extensive research has been conducted on the devices for producing PET radionuclides, and more recently, several manufacturers have begun developing machines which supply lower bombarding energies and higher beam currents. Research involving the associated target material to be used with such devices has not been all that extensive. Typical of the art of PET devices and target materials are disclosed in the following U.S. Pats:
______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 2,579,243 A. F. Reid Dec. 18, 1951 2,868,987 Salsig et al. Jan. 13, 1959 4,752,432 Bida et al. June 21, 1988 5,037,602 Dabiri et al. Aug. 6, 1991 5,135,704 Shefer et al. Aug. 4, 1992 5,280,505 Hughey et al. Jan. 18, 1994 5,345,477 Wieland et al. Sept. 6, 1994 ______________________________________
The U.S. Pat. No. 2,579,243 patent discloses a method for producing of radioactive isotopes which includes the use of a solid sodium metaborate target to provide radioactive sodium.
The U.S. Pat. No. 2,868,987 patent teaches a recirculating liquid target but does not indicate any particular target material.
The U.S. Pat. No. 4,752,432 patent teaches a device and process for producing nitrogen-13 radionuclides from a carbon-13/fluid slurry. The target material is held in position by at least a target window and frits. The frits are fine filters that allow water to pass through but do not allow passage of carbon powder of the target material.
The U.S. Pat. No. 5,037,602 patent teaches a radionuclide production facility for use with PET. The device utilizes a radio frequency quadruple linear accelerator. A particular target material is not taught.
The U.S. Pat. No. 5,135,704 patent teaches a radiation source and an accelerator. Again, a particular target is not taught.
The U.S. Pat. No. 5,280,505 patent teaches a method and apparatus for generating isotopes from a frozen target material. A thin surface layer of the target is frozen and the target is bombarded. The target material is isotopically enriched and when the desired quantity of isotope has been produced, the target is processed to extract the isotopes.
The U.S. Pat. No. 5,345,477 patent teaches a device and process for the production of nitrogen-13 using an ethanol solution target. The target solution is bombarded and the resulting radioactive effluent is subsequently washed from the target chamber by additional target solution. The radioactive effluent is purified and collected for use. The target produces only nitrogen-13 isotopes.
It is an object of the present invention to provide a process for producing radionuclides using a porous carbon target wherein the target, upon being bombarded, produces more than one type of radionuclide.
It is another object of the present invention to provide a process for producing radionuclides using a porous carbon target wherein the target is self supporting.
Further, it is another object of the present invention to provide such a process wherein the dimensions of the pores and the fibers of the porous carbon target can be specifically tailored.